There are many hydraulic applications in which a signal from a remote source such as an electric force motor is used to cause hydraulic response in a hydraulic control valve. Other workers in the prior art have utilized control pressure networks for establishing a movement in the main spool of the hydraulic valve in response to a movement in a remote control motor. For instance, the patent to W. C. Moog, Jr. U.S. Pat. No. 2,625,136, issued Jan. 13, 1953, discloses a pilot stage circuitry in which a half-bridge pilot circuit with a stationary nozzle is disclosed. In the Moog patent, the torque motor is a force generating device whereas in the instant invention, a displacement-type force motor is used. In Moog, the control pressure P.sub.c is fed back to the armature via a nozzle bore and reacts with the torque motor and reaction spring to achieve a constant P .sub.c regardless of the pilot pressure P.sub.s magnitude. In the instant invention, the control pressures vary with pilot supply pressure since P.sub.c is used as a feedback parameter. U.S. Pat. No. 3,410,308, issued to W. C. Moog, Jr. on Nov. 12, 1968, U.S. Pat. No. 3,430,656, issued Mar. 4, 1969 to J. W. Hawk, and U.S. Pat. No. 2,934,765, issued Apr. 26, 1960 to T. H. Carson, are also of interest.
Another patent of interest is that to E. C. Jupa, issued Mar. 7, 1961, U.S. Pat. No. 2,973,746, which shows a bridge network. In Jupa, the adjustable nozzle is stationary and not attached to the main spool as in the instant invention. Thus, Jupa does not incorporate a moving nozzle with a one-to-one position feedback. Jupa also has two variable orifices. The flapper nozzle, of course, is adjustable and his needle valve, on the end of the spool, is also adjustable.